1. Field of the Invention
This invention pertains generally to power-line networks, and more particularly to allocating bandwidth between virtual overlapping networks operating over the same physical power-line network.
2. Description of Related Art
Power-line communication (PLC) is being increasingly adopted as a standard network technology, in particular with regard to the consumer electronics market. Products employing proprietary signaling formats have been known for some time, and the current trends toward standardization have seen the marketing of standard bridge, router, and other PLC network based products.
FIG. 1 illustrates a conventional PLC network shown connecting three homes H1, H2, H3 to a distribution transformer, such as a 220 VAC service by means of a neutral N and two phase legs L1 and L2. It can be seen in the right of the figure how the power is distributed through a breaker panel to individual outlets within the homes or offices.
FIG. 2 depicts an equivalent circuit representing the PLC network based within the home power distribution example shown in FIG. 1. Resistive and capacitive loads are shown distributed along the network. It will be readily appreciated from viewing these figures that the homes share the PLC bandwidth and that data communicated between PLC network connected devices within one home will be available for reception at the other homes on the same segment of the power distribution grid, posing a security threat.
Issues surrounding the use of PLC networking include both security and bandwidth utilization. To overcome security issues it is most preferable to encrypt signals being passed over the PLC network. Communication over the PLC network is facilitated by giving each device connected to the PLC network a unique ID. Communication between devices requires that the ID of a destination device be entered. The common key is encrypted with the ID and sent to the first device. All the devices in the same home share the same common key and encrypt communications with the key. A neighbor cannot decrypt the communications without the common key, and each home (or entity connected to a power line that shares a distribution transformer) uses its own common key. A common key is therefore utilized for communicating between devices on each virtual network and a unique ID (at least unique within the confines of the virtual network) identifies each device within the virtual network.
The use of key based encryption is similar to encryption utilized within a VPN (Virtual Private Network). In VPN, two remote nodes communicate through a public network (i.e. the Internet) using encryption. Although only one physical network exists, multiple overlapping virtual networks operate over it.
FIG. 3 illustrates multiple overlapping virtual networks on a power line, PL, with three devices shown connected within a home establishing a first virtual network I, another three connection nodes in another home establishing a second virtual network II, and a final three devices on connection nodes in a third home establishing a third virtual network III. It should be appreciated that the number of devices on each virtual network may vary. With each virtual network configured with its own common key, no communication typically takes place between the virtual networks. As utilized herein the term “network” will be generally considered to mean a virtual overlapping network, and not the physical network, unless specifically indicated. The physical network is called the power line or the bus.
Another issue on present-day PLC network installations is access method. Typically, CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is utilized as it is in an Ethernet implementation. For a device to transmit, it first senses the state of the network bus. If the bus is idle, the transmission may proceed. If the bus is busy, transmission is deferred until the end of the current transmission. After deferring to a transmission, the device starts priority contention followed by a random backoff. CSMA/CA is simple and easy to connect, however, it is not generally well suited for use with an isochronous transmission, such as AV stream (audio and/or video stream), as it provides no guarantees that the data will be sent to the destination within the time necessary for providing uninterrupted display of the stream.
The use of multiple overlapping networks complicates the issue of access on CSMA/CA, because CSMA/CA provides access on a first come first serve basis. Consequently, the home that first accesses the PLC network could exclusively occupy a majority of the PLC bandwidth, for example if communicating a high definition video signal on the network. With a conventional CSMA/CA implementation, it is not possible for those which subsequently access the network to recover bandwidth from those which access it initially and retain their allotted bandwidth. This first-come first-serve allocation does not provide an equitable arrangement for many network applications, such as that of homes sharing the bandwidth of a power-line network connecting to a single distribution transformer.
Utilizing the IEEE 1394 bus standard would guarantee isochronous communications, however, it also provides bandwidth on a first-come first-serve basis. Therefore, no device can take time slots by force when the bus bandwidth is fully occupied. Furthermore, IEEE 1394 has no provisions for use on overlapping networks.
Therefore, a need exists for a system and method that provides equitable bandwidth allocation on overlapping networks, such as multiple virtual networks sharing a portion of a physical power-line. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previously developed power-line networking solutions.